The current invention is generally related to terminal communication, and more particularly related to the terminal communication method and system for a code division multiple access protocol.
In wireless or radio communication systems, in order for one caller to talk to another, mobile or portable communication units are temporarily connected via at least one base station. If a calling mobile unit is located inside a service area of one base station and a receiving mobile unit is located inside a service area of another base station, at least two base stations are involved in transmitting information between the two mobile units. On the other hand, if two mobile units are located in the same service area, one base station is involved. Since a large number of calls is local or within the same service area, the resources at a base station are heavily utilized by these local calls. In order to preserve the capacity to handle calls at the base station, in prior attempts, local calls are made directly between the two mobile communication units without going through a base station. To understand how these direct local calls between the two mobile communication units are made, one has to understand multiple access techniques that are used in wireless communication systems.
Multiple access techniques generally increase the capacity in number of concurrent communication lines between any two mobile communication terminals such as cellular telephones. One multiple access technique is time division multiple access (TDMA). The TDMA technique in general limits an amount of access time for each terminal communication unit so that a number of concurrent calls between terminal communication terminal units increases. TDMA may require that each cell to have a different frequency. Another system is based upon a code division multiple access (CDMA) technique which shares the same frequency among communication units but uses a unique code or function such as a Walsh code for each communication line to digitize data. In general, the coded digital communication signals use quasi-orthogonal bit sequences to decrease mutual interference when they are summed for transmission. Because of the above digital coding, user capacity is increased.
For the direct communication between mobile units using a TDMA technique, U.S. Pat. No. 5,515,366 or the corresponding Japanese Patent Laid Publication Hei 8-204683 discloses the use of time slots that are not used by the communication between a base station and actively communicating mobile units. Although the use of unused time slots is possible for the direct local communication between mobile units, a number of such direct local calls in one service area is limited. This is because when a plurality of the direct local calls takes place within the same service area, it is a complex task for the mobile units to find the available time slots in a coordinated manner.
Similarly, Japanese Patent Laid Publication Hei 8-294170 disclosed direct local calls between mobile units in the personal handy phone system (PHS), which utilizes unstable cyclic channel scanning. Because the PHS system uses the time division duplex, a precise timing technique is necessary and as the distance between the two mobile units in direct communication increases, a larger amount of guard time is also necessary. The long guard time does not allow a large number of concurrent direct local calls within the same service area.
Furthermore, Japanese Patent Laid Publication Hei 6-296263 and Hei 5-102921 disclose other direct communication between terminal devices such as a hand held cordless phone unit and a base unit.
The CDMA techniques have been used in the IS-95 standard, which has been adapted by the Telecommunications Industry Association. In accordance with the IS-95 standard, a terminal communication unit such as a cellular telephone establishes a bi-directional link with one or more base stations via the use of radio frequency electromagnetic signals. Each bi-directional link consists of a forward link which is transmitted at one frequency by the base station to the mobile terminal unit and a reverse link which is transmitted at another frequency by the mobile terminal unit back to the base station. In other words, the bi-directional link is frequency division duplex (FDD). Each base station transmits a pilot signal having a common pseudo-random noise (PN) spreading a code that is offset in code phase from the pilot signal of other base stations. Although current terminal communication units using the CDMA technique alone cannot be used for the above described direct local calls, these terminal communication units can be used as a part of the direct local call systems without affecting or modifying the current CDMA-based IS-95 standard.
It is desired to promote direct local calls between mobile communication units in the CDMA-based system so as to reduce the load on a base station to handle cellular calls. As a result, the capacity for the user calls in the CDMA-based system will increase.
In order to solve the above and other problems, according to a first aspect of the current invention, a method of providing an optional direct communication between terminal communication units according to code division multiple access which is also used for communication between the terminal communication units via a base station in a communication network, includes the acts of: determining currently used identification information for the code division multiple access surrounding a first terminal communication unit, the identification information being assigned from a set of predetermined unique identifiers; selecting an unused one of the predetermined unique identifiers as a temporary unique identifier for direct communication between the first terminal communication unit and a second terminal communication unit; and establishing the direct communication between the first terminal communication unit and the second terminal communication unit according to the code division multiple access using the temporary unique identifier.
According to a second aspect of the current invention, a system for providing an optional direct communication between terminal communication units according to code division multiple access which is also used for communication between the terminal communication units via a base station in a communication network, including the acts of: attempting to establish direct communication between a first terminal communication unit and a second terminal communication unit according to the code division multiple access; and based upon the attempt, establishing communication between the first terminal communication unit and the second terminal communication unit via the base station in the communication network.
According to a third aspect of the current invention, a system for providing an optional direct communication between terminal communication units according to code division multiple access which is also used for communication between the terminal communication units via a base station in a communication network, includes: a first terminal communication unit for determining currently used identification information for the code division multiple access surrounding the first terminal communication unit, the identification information being assigned from a set of predetermined unique identifiers, the first terminal communication unit selecting an unused one of the predetermined unique identifiers as a temporary unique identifier; and a second terminal communication unit capable of communicating with the first terminal communication unit via the base station, the first terminal communication unit and the second terminal communication unit establishing the direct communication between the first terminal communication unit and the second terminal communication unit according to the code division multiple access using the temporary unique identifier.
According to a fourth aspect of the current invention, a system for providing an optional direct communication between terminal communication units according to code division multiple access which is also used for communication between the terminal communication units via a base station in a communication network, includes: a first terminal communication unit attempting to establish direct communication between the first terminal communication unit and a second terminal communication unit according to the code division multiple access; and in response to a failure in the attempt, a base station located near the first terminal communication unit and the second terminal communication unit establishing communication between the first terminal communication unit and the second terminal communication unit via the base station in the communication network.